Tabled of analyses of coals from the Pennsylvania bituminous areas show that the proportion of volatile combustible matter decreases toward the east, though the rate of decrease is not regular and differs in the different beds. The decrease is even more marked in that portion of the state lying eastward from the bituminous areas, for there one finds the passage from semi-bituminous to the hard dry anthracite of the Middle fields.
A general knowledge of the features and relations of the several coal fields or geologic basins in Pennsylvania, as well as of their extensions toward the south, is absolutely essential to an intelligent discussion of the cause of the decrease in volatile. The portions of these basins or areas lying within Pennsylvania was described by Professor H. D. Rogers in his final report on the geology of the state, to which the reader . . .